Not sure about the gravel. I had pieces of slate for my beardie to keep her toe nails down. I'll eventually add a rock or two for him to climb on as it seems he LOVES to climb up stuff. His 3 passions are digging tunnels in the aspen and popping his head up in random places, climbing his half log or giant driftwood, and windshield washing the doors or wedging himself between the door and litter dam sides and inchworm his way up to the top of the cage lol. He definitely has a lot of personality. It's really funny when you walk by and startle him when hes got his head buried in the aspen and digging. He pops out, huffs up and stares at me. Then he must realize its me or something as he calms down and goes back to digging.